A method was developed for the determination of aluminum in sea water using oxine as a reagent. Extraction of aluminum oxinate by chloroform from acidic solution was impeded by the presence of fluoride in sea water. The fluoride Interference was less severe in basic solution and it was possible to extract aluminum oxinate from sea water at a pH of 8 with no loss of sensitivity due to the presence of fluoride. Iron and copper were complexed with cyanide in reducing solution and manganese oxinate was removed by extracting it from the chloroform into an aqueous acidic solution. Other interfering ions in sea water were present in amounts too small to be significant. The absorbancy of the aluminum oxinate complex was measured at 395 mμ and compared with a calibration curve. The aluminum concentration in sea water ranged from 2-42 μg./l. Values for coastal water were higher than for oceanic water. / Science, Faculty of / Chemistry, Department of / Graduate

By anodic oxidation, an aluminum plate can be covered with an amorphous or crystalline oxide layer, depending on the electrolyte used. The amorphous layer, obtained in a solution of oxalic or sulphuric acid, has a porous structure. However, the pores do not go right down to the aluminum as has been shown by many investigators, but end in a solic insulating layer, the thickness of which may be determined by capacity measurements. Corresponding to a given temperature and solic concentration of the electrolytic solution and a given formation current density, there is only one final capacity obtainable. Increasing the concentration, or temperature, or decreasing the current density, increases the final capacity obtainable. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Slip line length measurements have been carried out on oriented single crystals of high purity aluminum to qualitatively check the predictions of a new theory of plastic flow in strain hardened metals. This theory states that the slip line length L will be a function of the stress, σ, the yield strength, Ty, and the magnitude of the variation in the obstacle spacing, Tv. To achieve this purpose, the specimens were prestrained at room temperature to the same stress level insuring that they had the same structure. They were then electropolished and given a small increment of strain at a temperature between 298°K and 4°K or a strain rate from ɛ = 1x10⁻⁴ /min to ɛ = 2x10⁻¹ /min. The slip line lengths for these increments were found to increase with increasing strain rate and to decrease with increasing temperature, in agreement with the theory. By applying the increment of strain in small, divisions, the slip line length was found to increase during the region of transient deformation following a quench. This increase in L was due to an increase in stress. Lowering the prestrain temperature showed that the slip line length depended on the structure parameter Tv. A low temperature prestrain resulted in a smaller Tv and therefore shorter slip lines. From the 4°K increment, the parameters characterizing the prestrained structure and the structure after the increment could be determined. Using equations of the theory, these values were related to the experimental slip line length data with good quantitative agreement. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

A large number of axially loaded specimens of 2024-T3 aluminum sheet alloy were fatigued to failure in alternating tension. The stress ratio was kept constant at .05 and maximum stresses were chosen to cause failure in the upper part of the S-logN curve where failure is by progressive hardening. The specimens were prepared in three ways, unpolished in which the rough edges were rounded, chemically polished in which the central section was polished chemically, and mechanically and chemically polished in which the central section was rubbed with emery paper then polished chemically. Macroscopic and microscopic examinations of chemically polished specimens tested at a maximum stress of 47.5 ksi were also made. Statistical analysis was used to fit experimental frequency distributions to the life values at each stress level, to determine the effect of the different polishing methods and to determine the effect of a light oil coating. Of the two tried, the Lognormal and the Weibull, the Weibull distribution provided a better fit and was easier to use than the Lognormal. For the three different polishing groups, the mechanically and chemically polished specimens gave the longest lives at all stress levels followed by the chemically polished then the unpolished specimens. Also both groups which received a final chemical polish showed S-logN curves with a much rounder knee than did the unpolished group. Coating the specimens with a light non-corroding oil resulted in all cases in an increase in life and in more scatter in the life values. The increases ranged from 20% to 62%, At the knee of the S-logN curve, all groups showed a bimodal. distribution in the life values. This was felt to be the result of a change in the failure mechanism such as the one postulated by Wood. Examination of the fracture surface and of small cracks which formed near the edges indicated that the failure occurred in two stages; nucleation and growth of a small non-distorting fatigue crack followed by transition to a rapidly propagating ductile crack. Observations of the failures showed that it took approximately 1000 cycles from the appearance of the first small crack to when the ductile crack had propagated through the section. Microscopic examination showed that the fatigue cracks were intercrystalline and grew on the surface along slip marking which formed ahead of the tip of the crack. The only effect the crystal structure had was in the direction of the slip band formation. There was no indication that the mechanism by which the cracks initiated was different than the one by which they propagated. The cracks initiated at the surface and grew through to the other side. Once they reached the other side a ductile crack formed and final failure soon followed. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

The substructure of pure aluminum and over-aged Al-4Cu has been varied by mechanical and thermal treatments. The nature of this substructure and its resistance to annealing has been studied, together with the effect of the substructure on tensile strength at ambient and elevated temperatures. It has been found that in at least some respects the response of the strength of the over-aged Al-4Cu to mechanical and thermal processing is very comparable to that of oxide-dispersion-strengthened alloys such as S.A.P. and Ni-ThO₂. The over-aged Al-4Cu is strengthened appreciably by cold work. Much of this incremental room-temperature strengthening can be removed by annealing at relatively low temperatures; i.e. temperatures at which the strength of cold worked pure aluminum is not lowered. In common with oxide-dispersion hardened alloys, the yield strength of cold-worked Al-4Cu at elevated temperatures (300°C or 0.62 Tm) is actually improved by a static anneal at 300°C before testing. This benefit increases with increasing amounts of prior cold work. Similar studies have been carried out with an S.A.P. extruded alloy (10 wt. % A1₂O₃) and comparable results have been obtained. Pure aluminum, Al-4Cu and S.A.P. materials have been examined by X-ray line profile analysis to determine the distribution of nonuniform lattice strain and the coherently-diffracting crystallite domain size. The X-ray data have been interpreted in terms of dislocation densities and configurations, and compared with direct observations made by transmission electron microscopy. An attempt has been made to account semiquantitatively for the strength of the deformed and annealed materials at ordinary and elevated temperatures in terms of available strengthening mechanisms. The 0.2 pet yield strengths of simple aged Al-4Cu alloys (no substructure) was found to be consistent with the Orowan model of dispersion-strengthening both at R.T. and at 300°C. The room temperature yield strength (ϭ0.2) of cold worked and annealed pure aluminum and A1-4Cu alloys was related to the subgrain diameter [symbol omitted] by the Hall-Petch equation: °0 2 = ϭ₀ + kg⁻½ where and k are constants. In such cases it was not believed that there was a contribution to strength from the Orowan mechanism. Similarly the 20°C yield strength of the S.A.P. alloy was associated with the fine dislocation substructure produced by thermo-mechanical treatments. The high temperature yield strength of Al-4Cu and S.A.P. was related to the polygonized substructure produced by static annealing, which was much finer and more stable in the case of the oxide dispersion-strengthened alloy. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Normal and acid aluminum sulphate solutions containing about 6.0 gr/1 of aluminum and up to 50 gr/1 SO₄⁼ were hydrolyzed until equilibrium was reached in the temperature region 125-250°C. Under the equilibrium conditions the only stable solid phase observed in equilibrium with a liquid phase of various compositions was basic aluminum sulphate with nominal formula 3A1₂0₃..4S0₃.9H₂O. A small portion of the ternary diagrams for the system A1₂O₃-SO₃-H₂O at 225°C and 250°C was constructed. A mixture of aluminum sulphate and other metal sulphates, K₂S0₄, Na₂S0₄, Li₂SO₄, FeSO₄ and CuSO₄ i.e. was hydrolyzed at 225°C in order to find the effect of these salts on hydrolysis. The overall hydrolysis reaction was found to occur according to the chemical equation: 6A1⁺⁺⁺+ 4HS0₄⁻ + 14H₂O ⃗ 3Al₂0₃.4S0₃.9H₂0 + 14H⁺ The equilibrium constants at 125, 150, 175, 200, 225 and 250°C were determined. Finally a mechanism for the hydrolysis of aluminum sulphate was proposed. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

No description available.

No description available.

No description available.

The aim of this research was to identify the effect of alloying additions and heat treatment on the localized corrosion mechanisms of AA7xxx alloys that have been grain refined with an Al-5Ti-1B master alloy. The major alloying elements, Zn (3.5 – 6.5 wt. %), Mg (1.5 – 2.5 wt.%), Cu (0 – 3 wt. %), and Ti (0.04 – 0.25 wt.%), were varied and ten AA7xxx aluminum alloys were cast, heat treated to the T4, T6, T79, T76, and T73 tempers, and studied extensively. Casting high integrity near net shaped AA7xxx components by introducing Ti and B into the melt to facilitate a non-dendritic microstructure produced a unique microstructure due to the phenomena of athermal nucleation, unconstrained growth, and solute field impingement. The three phenomena listed above create three microstructural regimes; dendritic area rich in Ti, interdendritic region lean in Ti, and grain boundary area rich in eutectic phases. The breakdown potential, Eb, in a detreated 0.5 M NaCl(aq) was determined for each alloy and heat treatment after 1 h at the open circuit potential. The effect of alloying element composition and heat treatment on Eb was examined and an empirical expression was created. It was determined that a semi-logarithmic relationship exists between Eb and the Zn/Cu weight ratio. Zn and Cu have opposing effects on Eb, where, Zn-depletion from the solid solution into the strengthening precipitates increased the Eb while Cu-depletion decreased the same. Cu-lean alloys have a continually increasing Eb from T4 to T6 and T7x temper conditions, while, Cu-rich alloys have no significant change in Eb with temper condition. The critical Zn/Cu weight ratio was determined to be approximately 5. Corrosion initiation mechanisms of a Cu-lean and Cu-rich alloy were studied using the dual beam FIB-SEM platform after 5 min of potentiostatic polarization in detreated 0.5 M NaCl(aq) at potentials of interest. The initiation mechanism of the Cu-rich alloy (alloy 3) was determined to be dealloying of the S-phase (Al2CuMg) along the grain boundary leading to intergranular corrosion. The surface of the Cu-lean alloy (alloy 6) after potentiostatic polarization above Eb showed three mechanisms of corrosion; corrosion domes, corrosion rings, and interdendritic corrosion. Corrosion rings were identified as the initiation mechanism, corrosion domes were determined to be metastable sites and not a precursor to further corrosion, interdendritic corrosion was determined to be the propagation mechanism. Interdendritic corrosion is the selective dissolution of the interdendritic region leaving the dendritic regime intact after immersion in a corrosive solution which is unique to these alloys grain refined with the Ti-B master alloy. Corrosion domes were shown to cause an active-passive region in the potentiodynamic polarization curve. Modified EXCO experiments were used to study the propagation mechanism in each of the alloys at each temper. All alloys and tempers were susceptible to interdendritic corrosion, however Cu-lean alloys showed less surface damage after 96 h of immersion in the modified EXCO solution. Alloys with a Zn/Mg weight ratio < 2 were susceptible to intergranular corrosion in the T6 temper, however, in the T4 and T7x temper the primary mode of corrosion propagation is interdendritic corrosion. Due to the bimodal distribution of the grain size, intergranular corrosion was only observed in the small grain areas. The extent of attack was more severe in the small grain regions with intergranular corrosion present than areas without leading to the conclusion that intergranular corrosion is more detrimental than interdendritic corrosion. / Thesis / Master of Applied Science (MASc)